The present invention relates to radiopaque markers and, more specifically, radiopaque markings that are physical vapor deposited onto graft material.
Prosthetic grafts are used to repair diseased or damaged vessels as well as to help maintain the patency of body lumens. One way of implanting a prosthetic graft within a body lumen involves open surgical repair of a damaged or diseased vessel. For example, open surgical repair of an abdominal aortic aneurysm (AAA) requires a large incision to be made through the abdominal wall. The patient""s internal organs are moved aside to provide the surgeon access to the aorta. The aorta is then cut, and the prosthetic graft is placed at the site of the aneurysm.
Open surgical repair of AAA and implantation of the prosthetic graft into patients who need such treatment is not always the preferred procedure. Many patients who suffer from AAA also suffer from other ailments and cannot endure such a highly invasive surgical procedure. Those who do undergo such an open surgical procedure typically need to stay in the hospital for several days and require several months of convalescence to fully recuperate.
Less invasive alternatives to open surgical implantation of a prosthetic graft exist. One example is a minimally invasive endovascular treatment of AAA using a catheter delivery system, such as the ANCURE(copyright) System developed and manufactured by Guidant Corporation. The use of the ANCURE(copyright) System requires making an incision to a femoral artery. A surgeon inserts the delivery catheter, which contains a compressed prosthetic graft, through the femoral artery and navigates the catheter through the patient""s vasculature to deliver the prosthetic graft to the site of the aneurysm, where the graft is implanted. The catheter is then removed. Similar endovascular procedures are used to implant prosthetic grafts in other body lumens.
One difficulty associated with endovascular procedures is navigating the delivery catheter through the patient""s vasculature. Vascular anatomy can be quite tortuous and narrow. The outer diameter (i.e., containing the profile) of the catheter graft is thus an important feature. There exists a general need to minimize the bulk of the graft in order to minimize the profile of the catheter.
In performing such endovascular procedures, a physician typically will use a fluoroscope to help navigate the catheter through the vasculature. The catheter typically will have several radiopaque markers thereon, particularly near the distal end where the graft is carried, so that the physician can see various points along the catheter under the fluoroscope. The graft itself typically has several radiopaque markers to assist the physician in positioning and orienting the graft within the vessel. The radiopaque markers on the graft also help the physician visualize the graft after implantation, to make sure that the graft remains in its proper place and has not collapsed or twisted or otherwise deformed.
Graft radiopaque markers generally are wires or coils made of a radiopaque metal or alloy, such as platinum, platinum-tungsten, or platinum-iridium, which are woven into or sewn onto the graft material. Alternatively, polymeric fibers coated or filled with radiopaque particles are sometimes woven into the graft material. Typically the weaving or sewing of such radiopaque markers onto the graft material is done by hand, a very time consuming and labor intensive procedure requiring highly skilled laborers. Radiopaque coils and wires also add undesirable bulk to the graft.
Physical vapor deposition (PVD) processes have been used to plate or deposit thin layers of metal onto metallic or semiconductor substrates. Metal layers on the order of a few microns or less can be formed using PVD processes such as vacuum evaporation and sputter deposition, and such processes can be readily scaled for large throughput manufacturing.
The primary difficulty in applying PVD to form radiopaque markings onto a graft is that typical PVD conditions may damage the graft material, making the graft material unsuitable for use as a graft. Vaporization of the radiopaque material requires high energy to be applied to the source, and material vaporized from the source would tend to transfer this energy to the graft material, which may cause localized melting or burning of the graft material where the vaporized material is deposited. Ionization of the radiopaque material, which may occur during vaporization, tends to generate ultraviolet radiation, which also may damage the graft material.
Given the high energies and generally harsh processing conditions under which physical vapor deposition occurs, PVD processes have not heretofore been considered for use with graft materials.
Physical vapor deposition of a radiopaque marking onto a graft is described. In one aspect, a method for physical vapor depositing a radiopaque marking onto a graft is provided. A graft is placed in a chamber that has therein a source of a radiopaque material. The chamber is evacuated, and the radiopaque material is vaporized from the source in the chamber. The vaporized material is deposited onto the graft to form a radiopaque marking. Another aspect of the present invention provides a graft having a physical vapor deposited radiopaque marking.